1. Field of the Invention
This invention relates to aftertreatment devices for treating engine exhaust streams, and more particularly relates to determining the time-temperature experienced in aftertreatment devices.
2. Description of the Related Art
Emissions regulations for internal combustion engines have changed rapidly in recent years. To meet the new regulations, many engine manufacturers have had to install aftertreatment devices to reduce emissions in the exhaust gases, or to condition the exhaust gases to assist other aftertreatment devices. For example, particulate filters remove soot from the exhaust gases of a diesel engine, and diesel oxidation catalysts are sometimes used to generate temperature in the exhaust gas to assist a particulate filter in oxidizing the soot off of the filter.
Most aftertreatment devices experience thermal cycles during the operations of the engine. The thermal cycles may be intentional, for example during the removal of soot from a particulate filter, or unintentional such as when the engine experiences large changes in the required workload for the engine. As the aftertreatment devices experience thermal cycles, the physical characteristics of the device can degrade over time. For example, stresses on the substrate of the device experience wear and thermal fatigue, while catalytic aspects of the device may experience thermal degradation and deactivation.
The combination of time and temperature experienced by the aftertreatment device is particularly difficult to detect. There are no direct measurements routinely used in real-time for applications to detect temperatures within an aftertreatment device. The internal temperatures of the device are the most significant in terms of degradation, and the most difficult in terms of measuring. Even when an aftertreatment device removed from an application for service and can be observed directly, there are no current techniques to estimate the time-temperature history of the device. Catastrophic failures, such as the melting of an aftertreatment device during an extreme temperature event, can often be detected visually. However, excessive device degradation due to high average temperatures the service life of the device cannot be detected using current technologies.
The current inability to measure the time-temperature history of aftertreatment devices limits the serviceability of these devices, increases the total cost of operating aftertreatment devices, and increases the possibility of an aftertreatment device failing unexpectedly and causing emissions increases. If an aftertreatment device is removed from an application and replaced with a cleaned aftertreatment device, there is currently a significant risk that an aftertreatment device with a dissimilar history and remaining service life will be installed as a replacement. Further, applications using aftertreatment devices will have to be designed with extra operating margin, in terms of catalyst loading and usable service life, to prevent failures because the operating history of a device cannot be measured. Finally, if a device is used excessively and experiences a non-catastrophic failure, there is currently no method to estimate this occurrence and failure or substandard operation can occur.